1. Field of the Invention
The present invention relates to a bulb socket and, in particular, to a socket for a wedge base bulb (no-cap bulb) or the like for use in an automobile lighting device and the like.
2. Related Art
With reference to FIGS. 14 to 16, there is shown a conventional bulb socket for a wedge base bulb. FIG. 14 is a perspective view of a bulb socket and a socket mounting hole, FIG. 15 is a section view of the periphery of the socket mounting hole into which a bulb socket with an integrally inserted bulb is mounted, and FIG. 16 is a section view to show how to mount the bulb socket into the socket mounting hole.
As shown in these figures, the conventional bulb socket includes a socket main body 2 which is formed of synthetic resin. The socket main body 2 includes a bulb insertion opening 3 which is opened forwardly and into which a wedge base bulb 5 can be inserted. Within the bulb insertion opening 3 there are stored a plurality of terminals 4 which respectively include mutually opposing contact hold pieces 4a. When the wedge base bulb 5 is inserted into the bulb insertion opening 3, the base portion 5a of the bulb 5 is clamped by these mutually opposing contact hold pieces 4a, thereby achieving electrical contact between lead wires exposed on the surface of the base portion 5a and the terminals 4.
Provided on the outer periphery of the socket main body 2 are a plurality of securing projections 7 which can be engaged in a bayonet-like manner with a socket mounting hole 9a formed in a lamp body 9, and a plurality of elastic flange portions 8 which extend obliquely toward the securing projection 7 side. The securing projections 7 and the flange portions 8 are respectively spaced a given distance from each other in the axial direction of the socket main body 2. As shown by the arrow line in FIG. 16, if the socket main body 2 is pushed into the socket mounting hole 9a with the securing projections 7 matched thereto and also the thus pushed-in socket main body 2 is rotated a given amount along the peripheral edge portion of the mounting hole 9a, then the peripheral edge portion of the mounting hole 9a can be held by and between the securing projections 7 and elastic flange portions 8. That is, the socket main body 2 with the integrally inserted bulb 5 can be fixed and held in the socket mounting hole 9a due to the elasticity of the elastic flange portions 8. Here, reference character 9b designates notches which are formed in the socket mounting hole 9a in such a manner that they can be matched to the securing projections 7a provided on the socket main body 2 side.
In the above-mentioned conventional socket hold structure using the elasticity of the elastic flange portions 8, the retaining capability of the socket main body 2 within the socket mounting hole 9a is not sufficient and the bulb socket cannot be mounted in or removed from the socket mounting hole 9a smoothly.
That is, the elastic flange portions 8 extend obliquely forwardly from the socket main body 2 so that they can cooperate together with the securing projections 7 to hold the peripheral edge portion of the socket mounting hole 9a. Additionally, the elastic flange portions have sufficient flexibility to allow for easy mounting and removal of the bulb socket. Due to this, however, clearances caused between the securing projections 7 and the associated root portions of the elastic flange portions 8 are far greater than the plate thickness of the peripheral edge portion of the socket mounting hole 9a, which results in the engagement between the socket main body 2 and socket mounting hole 9a being loosened.
If the plate thickness of the elastic flange portion 8 is increased to thereby enhance the rigidity (that is, reduce the flexibility) of the elastic flange portion 8 as well as to thereby apply a greater holding force between the securing projection 7 and the elastic flange portion 8, then it is possible to prevent the disengagement between the socket main body 2 and socket mounting hole 9a. However, the increased thickness of the elastic flange portion 8 also increases a frictional resistance when the socket main body 2 is rotated along the socket mounting hole 9a, which makes it difficult to mount and remove the socket main body 2. Especially, when mounting the socket main body 2 into the socket mounting hole 9a, as shown in FIG. 16, it is generally necessary to push in the socket main body 2 up to a front position where the securing projections 7 are moved beyond the peripheral edge portion of the socket mounting hole 9a, which requires a great force when mounting the socket main body 2 in the socket mounting hole 9a. Also, in the winter season or in cold districts, since the elasticity of resin (that is, the flexibility of the elastic flange portion 8) is lowered, it is even more difficult to mount and remove the socket main body 2.
On the other hand, if the thickness of the elastic flange portion 8 is decreased to thereby enhance the flexibility thereof, then the socket main body 2 can be mounted and removed smoothly with a slight force. However, since the holding force of the peripheral edge portion of the socket mounting hole 9a by the elastic flange portions 8 is correspondingly reduced, the engagement between the socket main body 2 and socket mounting hole 9a can be loosened easily. Also, as the thickness of the elastic flange portion 8 is reduced, there is a greater likelihood that the elastic flange portion 8 will experience fatigue and break. This is particularly true in the winter season or in cold districts. Specifically, when pushing the socket main body 2 into the socket mounting hole 9a, there is a possibility that a bending stress equal to an allowable stress or greater will be applied to the elastic flange portion 8 by mistake and thus the elastic flange portion 8 can be broken. In short, if the thickness of the elastic flange portion 8 is reduced, then the elastic flange portion 8 is poor in durability.